Clinical evaluation of patients with acute scrotal pain is often unreliable. The main concern is the distinction of testicular torsion from other causes of scrotal pain. Testicular torsion leads to ischemia, and salvage rates are inversely proportional to the duration of ischemia. While color Doppler ultrasound is a valuable tool in the imaging evaluation of acute scrotal symptoms, its use in children is often limited by an inability to depict flow in testes of small volume. Recently developed contrast-enhanced US techniques result in significantly increased sensitivity to flow in small blood vessels. The proposed study will test the hypothesis that the novel technique of contrast-enhanced pulse inversion US imaging will improve detection of acute vascular compromise of the testis in a rabbit model compared to conventional color Doppler US imaging. The specific aims include: (1) comparing the accuracy of measurements of testicular perfusion obtained with contrast-enhanced pulse inversion US imaging to those obtained with radio-labeled microspheres, a standard method of blood flow measurement; and (2) comparing qualitative assessment of testicular perfusion based on a review of contrast-enhanced pulse inversion US images to qualitative assessment of testicular perfusion based on a review of conventional color Doppler US images using perfusion measurements obtained with radio-labeled microspheres as a "gold standard." Qualitative assessment of all US images will be performed by two independent readers blinded to experimental conditions. This study has the potential to result in greater accuracy in the assessment of testicular perfusion compared to conventional US techniques, which should expedite clinical implementation of a promising diagnostic tool in the pediatric population. This would ultimately lead to improved patient care, including prevention of and reduction in the loss of fertility related to the delayed diagnosis of testicular torsion.